In brief, if the FBI gets its hands on the golden key, then the protections introduced in the second draft of the Bill giving Apple a defence when the Secretary of State orders them to hand over a decryption key, if it is not practical or it is illegal in Apple's home country, get taken away. With the key in existence it becomes practical to hand it over. With the key lawfully in the FBI's hands it becomes lawful for Apple to hand it over, in secret, to the requisite approved UK authorities in possession of the Secretary of State's warrant, (duly checked by a judicial commissioner, under the dual lock process, to ensure procedures have been followed).